The present invention generally relates to imaging devices and specifically to the reduction or elimination of toner leakage past toner seals in imaging devices through the use of capacitive or static charge.
Currently there are several types of technologies used in printing and copying systems. Electrophotographic printing devices such as laser printers and copiers use toner particles to form a desired image on a print medium, which is usually some type of paper. Once the toner particles are applied to the paper, the paper is advanced along a paper path to a fuser. In many printers, copiers and other electrophotographic printing devices, the fuser includes a heated fusing roller engaged by a mating pressure roller. As the paper passes between the rollers, toner particles are fused to the paper through a process of heat and pressure.
FIG. 7 is a diagram of typical laser printing device 700 employing an electrophotography (EP) process. For monochromatic printing, a single color of toner particles 701 are held in toner supply hopper 702. Toner particles 701 are typically small plastic (e.g., styrene) particles on the order of 5 microns (10-6 meter) in size. Agitator (or stirring blade) 703 is typically made of plastic such as mylar and ensures toner particles 701 are uniformly positioned along developer sleeve 705 while inducing a negative charge onto the toner particles 701 in the range of xe2x88x9230 to xe2x88x9280 micro coulomb per gram (xcexcc/g). Developer sleeve 705 rotates in a counterclockwise direction about an internal stationary magnet 704 acting as a shaft. Toner particles 701 are attracted to the rotating developer sleeve 705 by the magnetic forces of stationary magnet 704. Doctor blade 706 charges the toner particles 701 and metes out a precise and uniform amount of toner particles 701 onto developer sleeve 705 as its outer surface rotates external to toner supply hopper 702. Developer sealing blade 707 removes excess toner particles 701 affixed to developer sleeve 705 as its outer surface rotates back into toner supply hopper 702 and prevents toner particles 701 from falling out of toner supply hopper 702 onto paper, along the length of developer sleeve 705.
Primary charging roller (PCR) 708 conditions organic photoconductor (OPC) drum 709 using a constant flow of current to produce a blanket of uniform negative charge on the surface of OPC drum 709. Production of the uniform charge by PCR 708 also has the effect of erasing residual charges left from any previous printing or transfer cycle.
A critical component of the EP process is OPC drum 709. OPC drum 709 is a thin-walled aluminum cylinder coated with a photoconductive layer. The photoconductive layer may constitute a photodiode that accepts and holds a charge from PCR 708. Initially, the unexposed surface potential of the OPC drum 709 is charged to approximately xe2x88x92600 volts. Typically, the photoconductive layer comprises three layers including, from the outermost inward, a charge transport layer (CTL), charge generation layer (CGL), and barrier or oxidizing layer formed on the underlying aluminum substrate. The CTL is a clear layer approximately 20 microns thick, which allows light to pass through to the CGL and controls charge acceptance to the OPC drum 709. The CGL is about 0.1 to 1 micron thick and allows the flow of ions. The barrier layer bonds the photoconductive layer to the underlying aluminum substrate.
Scanning laser beam 710 exposes OPC drum 709 one line at a time at the precise locations that are to receive toner particles 701 (paper locations which correspond to dark areas of the image being printed). OPC drum 709 is discharged from xe2x88x92600V to approximately xe2x88x92100V at points of exposure to laser beam 710, creating a relatively positively charged latent image on its surface. Transformation of the latent image into a developed image begins when toner particles 701 are magnetically attracted to rotating developer sleeve 705. Alternatively, if a nonmagnetic toner is used, developer sleeve 705 may comprise a developer roller to mechanically capture and transport toner particles 701. In this case, an open cell foam roller may be included to apply toner particles 701 to developer sleeve 705. The still negatively charged toner particles 701 held by developer sleeve 705 are attracted to the relatively positively charged areas of the surface of OPC drum 709 and xe2x80x9cjumpxe2x80x9d across a small gap to the relatively positively charged latent image on OPC drum 709 creating a xe2x80x9cdevelopedxe2x80x9d image on the OPC drum 709.
Paper to receive toner from OPC drum 709 is transported along paper path 711 between OPC drum 709 and transfer roller 712, with the developed image transferred from the surface of OPC drum 709 to the paper. The transfer occurs by action of transfer roller 712 which applies a positive charge to the underside of the paper, attracting the negatively-charged toner particles 701 and causing them to move onto the paper. Wiper blade 713 cleans the surface of the OPC drum 709 by scraping off the waste (untransferred) toner into waste hopper 715, while recovery blade 714 prevents the waste toner from falling back onto the paper. Fusing occurs as the paper, including toner particles 701, are passed through a nip region between heated roller 716 and pressure roller 717 where the toner particles 701 are melted and fused (or xe2x80x9cbondedxe2x80x9d) to the paper. Heated roller 716 and pressure roller 717 are together referred to as the fuser assembly.
Referring to FIG. 8, color printing follows a slightly different procedure in that a foam roller 801 (1 of 4) is used to deposit particular color toner particles (e.g., CMYK: cyan, magenta, yellow and black) onto developer roller 802 for the corresponding color. Foam roller 801 is made of an open cell foam with bias, while developer roller 802 has a coated exterior charged with a bias of between xe2x88x92350 to xe2x88x92450 VDC.
One design consideration with EP imaging devices, such as laser printers, is to minimize the leakage of toner particles 701 from a toner supply hopper 702. Leakage sometimes occurs at the ends of developer sleeve 705 (FIG. 7). Several methodologies and arrangements have been used to reduce or eliminate toner leakage from the ends of developer sleeve 705. Some printers employ a foam or felt mechanical seal at the ends of developer sleeve 705 as a physical barrier to prevent toner particles from slipping past the interface between developer sleeve 705 and toner supply hopper 702. Alternatively, when the toner exhibits magnetic properties, such as in many black and white printers, magnetic seals may be provided at the ends of developer sleeve 705 to attract monochromatic toner particles and create a physical barrier, consisting of the monochromatic toner particles, to prevent additional particles from leaking. Unfortunately such techniques are generally inapplicable to the non-magnetic type of toner used, for example, in most color printers and copiers.
Accordingly, a need exists for a structure and method for reducing toner leakage in a toner cartridge.
The present invention includes a method of sealing a toner supply to a developer sleeve, the method including the steps of introducing a static-electric charge on toner particles to create charged toner particles and inducing an attractive charge onto each end of the developer sleeve. The static-electric charge and the attractive charge result in toner particles being attracted to the ends of the developer sleeve which create a barrier of charged toner particles to prevent leakage of the charged toner particles.
Another embodiment of the present invention is directed at a sealing apparatus for sealing an interface between a toner supply and a developer sleeve. In this embodiment the invention includes electrostatically charged toner particles and a charged seal on each end of the developer sleeve.